In modern society, many diseases are not only caused by physiological factors, but also by psychological factors. Human heart does not beat with a stable rate, and the variability is called “heart rate variability (HRV).” HRV can have considerable fluctuation even in calm and stable state. We can derive activity of autonomic nervous system though analysis of HRV.

Principle of heart rate variability algorithm

The time interval between heartbeats is unstable. The variation is called heart rate variability (HRV). HRV analysis is a method of analyzing heartbeat rate variability. HRV can be calculated by computing time interval of P wave of photoplethysmography, and the analysis can be performed in time domain and in frequency domain. High frequency domain usually reveals the degree of activation of parasympathetic nerve; while low frequency domain reveals the degree of activation of sympathetic nerve.